MH itself can be prepared by reaction of isopropenyl methyl ether with 2-methyl-3-buten-2-ol as described by G. Saucy and R. Marbet in Helv. Chim. Acta 1967, 50, 2091-2095.
DMOE as well as tetrahydrolinalool (THLL, 3,7-dimethyl-octan-3-ol) are base products for the flavour and fragrance industry. DMOE, a colourless to pale yellow liquid, has a rose odour and is used in a variety of perfumery applications. It is seen as an alternative to geraniol.
DMOE and THLL are furthermore possible intermediates for isophytol (see e.g. P. Karrer, K. S. Yap, Helv. Chim. Acta 1940, 23, 581), which may be used to manufacture vitamin E (see Ullmann's Encyclopedia of Industrial Chemistry, Editors: Barbara Elvers, Stephen Hawkins, 5th completely revised edition, VCH Verlagsgesellschaft mbH, D-69451 Weinheim, 1996, Volume A27 (Thor to Vita), Chapter 4.11.2-4.11.5, page 484-488; especially Chapter 4.11.2 (page 484-485)).
6,10-dimethyl-5-undecen-2-one may be manufactured starting from DMOE according to processes known to the person skilled in the art like e.g. described in U.S. Pat. No. 2,783,257 (see scheme in column 1) and DE-AS 1 193 490 (see example 10). 6,10-Dimethyl-5-undecen-2-one may then be hydrogenated to obtain hexahydropseudoionone (HPI) (see U.S. Pat. No. 2,783,257: column 2, line 58-64), which may be further reacted to (iso)phytol according to processes as e.g. disclosed in Appl. Catal. 2005, 280, 55-73 and Catal. Today 2007, 121, 45-57.
Processes for the manufacture of THLL and DMOE are already known:
P. Karrer and K. S. Yap (Helv. Chim. Acta 1940, 23, 581-584.) describe a procedure for the synthesis of THLL starting from MH. The MH reduction was carried out in the presence of a Pt catalyst, yields were not given. The resulting methylheptanone (MHA) was ethynylated using ethyne and sodium amide. 3,7-Dimethyl-octin-1-3-ol was catalytically reduced in presence of a Pt catalyst. The disadvantage of the procedure is that stoichiometric amounts of the ethynylation agent are used, the hydrogenations are performed with an expensive catalyst, no yields are given (the analysis is not discussed), the reactions are carried out in solvents, and low yields are obtained if we assume that 20 g of MH give 8 g of THLL, based on the experimental procedures reported. The THLL obtained is used for the synthesis of isophytol.
According to U.S. Pat. No. 2,780,658 DMOE (named as 1,5-dimethyl-1-vinyl-1-hexanol) is synthesized starting from MHA which is ethynylated in presence of sodium in liquid ammonia followed by Lindlar hydrogenation in the presence of a catalyst which is Pd/Pb on CaCO3. The hydrogenation was carried out in petroleum ether at 20-30° C. For the hydrogenation of 308 g of the starting material 20 g of the catalyst (s/c≈15) were required.
A similar procedure was claimed in GB 788,301. MHA was ethynylated in ether in presence of ammonia using sodium and ethyne followed by Lindlar hydrogenation in ligroin as solvent. The ethynylation was described to proceed in 82.2% yield.
I. N. Nazarov et al. described in Seriya Khimicheskaya 1957, 1267-1270 and in Zhurnal Obshchei Khimii 1958, 28, 1444-1448 the semi hydrogenation of alkynols in presence of Pd on CaCO3. MHA was ethynylated in 87% yield in presence of solid KOH at 0-20° C. at 5-8 atmospheres, followed by hydrogenation (90%), no conditions were given.
A. Other et al. described in Helv. Chim. Acta 1959, 42, 2577-2584 the Pd/CaCO3 (5% Pd loading) catalyzed hydrogenation of MH to MHA at 34 atm pressure, followed by sodium acetylide treatment to give the corresponding alkynol and Lindlar hydrogenation to DMOE (named as dihydro-linalool).
F. J. Bröcker et al. claimed the preparation and application of hydrogenation catalysts. In EP-A 412 415 the preparation of a Pd catalyst on a support by metal vapour deposition was claimed (300-800° C.), and especially the hydrogenation of 3,7-dimethyl-oct-1-in-3-ol (named as hydro-dehydrolinalool (HDHL)) to DMOE (named as hydro-linalool (HLIN)) was demonstrated (examples 2 and 3: 100% conversion, 99.3%-99.5% selectivity).
EP-A 754 664 describes the partial hydrogenation of alkynes using a solid-bed catalyst as described in EP-A 412 415, whereby the Lindlar hydrogenation was carried out in presence of CO (10-180 ppm).
In EP-A 1 110 932 the above applications are combined and more examples are presented. A similar procedure of alkyne hydrogenation in presence of CO was carried out.
EP-A 816 321 claimed the synthesis of MHA by aldol reaction of acetone and isovaleraldehyde in presence of hydrogen and a conventional hydrogenation catalyst at 15-150° C. and 1-100 bar, (example 3: Pd/C). For the ethynylation of MHA standard protocols were used (example 3, step c, 2 hours, 4-6° C., KOH in water, ammonia). Solvents like NMP, DMSO, and DMF had to be used. These solvents are difficult to separate from the product, (and) especially they could have a negative impact on flavour and fragrance applications. The Lindlar hydrogenation was carried out in a solvent, e.g. hexane, heptane, at 1-130° C. and at 1-50 bar. The preferred catalyst was Pd on CaCO3 (selectivity 95-96%, conversion 97.3-99.7%). In the examples (step 3c, page 20) the Lindlar hydrogenation was carried out in hexane.
The object of the present invention was to provide a process which may be used for the industrial production of DMOE, i.e. a process which is economic. Furthermore, the process according to the present invention should not have the disadvantages of the processes of the prior art.
A preferred object of the present invention was also to achieve a selectivity >90% at a conversion of >95%.